i. Yes indeed, just delete that code. Do you still want white space above the center column? If that's the case I can help with that. Otherwise just delete it.
ii. Many ways to do this. Open your sidebar.php files and in between these two lines of code:
<div id="sidebar">
<ul class="sidebar_list">
Stick your <img src="xxx"> code.
Just make sure your image is the same width of the column (210px i think) or you'll cause some issues.
If you notice stuff dropping down, your image is probably too wide.
That's really all there is to it unless you want them to be random images or something.
You could also use css and modify these objects to have background images that don't repeat and start at the top of the columns:
#sidebar { width: 210px; padding: 0 0 0 15px; float: right; }
#l_sidebar { width: 210px; padding: 0 0 0 15px; float: left; }
For working with background images: (very easy, basic CSS) http://www.w3schools.com/css/css_background.asp